There were several Popes who had resigned, but none have done so since the 1400s.
The most well known resignation was of Pope
Celestine V. He established in church law that Popes could indeed
resign of their own free will. After leaving the papacy Celestine lived two more years as a hermit. Pope Boniface VIII then imprisoned him and Celestine died while in prison. Some historians believe that Celestine was murdered by Boniface.
The last resignation of a Pope was in 1415, when Gregory XII resigned in order to help bring an end to the Western Schism.